Drug delivery devices for setting and dispensing a single or multiple doses of a liquid medicament are as such well-known in the art. Generally, such devices have substantially a similar purpose as that of an ordinary syringe.
Drug delivery devices, in particular pen-type injectors have to meet a number of user-specific requirements. For instance, with patient's suffering chronic diseases, such like diabetes, the patient may be physically infirm and may also have impaired vision. Suitable drug delivery devices especially intended for home medication therefore need to be robust in construction and should be easy to use. Furthermore, manipulation and general handling of the device and its components should be intelligible and easy understandable. Moreover, a dose setting as well as a dose dispensing procedure must be easy to operate and has to be unambiguous.
Typically, such devices comprise a housing or a particular cartridge holder, adapted to receive a cartridge at least partially filled with the medicament to be dispensed. The device further comprises a drive mechanism, usually having a displaceable piston rod which is adapted to operably engage with a piston of the cartridge. By means of the drive mechanism and its piston rod, the piston of the cartridge is displaceable in a distal or dispensing direction and may therefore expel a predefined amount of the medicament via a piercing assembly, which is to be releasably coupled with a distal end section of the housing of the drug delivery device.
The medicament to be dispensed by the drug delivery device is provided and contained in a multi-dose cartridge. Such cartridges typically comprise a vitreous barrel sealed in distal direction by means of a pierceable seal and being further sealed in proximal direction by the piston. With reusable drug delivery devices an empty cartridge is replaceable by a new one. In contrast to that, drug delivery devices of disposable type are to be entirely discarded when the medicament in the cartridge has been completely dispensed or used-up.
Document U.S. Pat. No. 8,357,120 B2 discloses for instance an injection device with a torsion spring and a rotatable display. There, a piston rod has a threaded outer surface that engages and co-operates with a threaded portion of the injection device. The piston rod is driven by a drive member that engages a groove in the piston rod. The axial movement of the piston rod is provided by rotating the piston rod in the threaded portion of the injection device. Furthermore, a locking member is located at a rather distal portion, hence close to a dispensing end of the injection device. It may extend along a cartridge or a cartridge holder comprising the medicament to be dispensed.
With typical drug delivery devices of pen-injector type, patients or users got used to set a dose and to subsequently induce a dose dispensing action by means of a dose setting member and a dose dispensing member, that are both located at a proximal end of the device. Taking the hand-held injection device in a closed hand, an injection procedure may then be simply triggered by depressing a proximally located dose dispensing member in distal direction by making use of a thumb.
It is therefore an object of the present invention to provide an improved drive mechanism of a drug delivery device allowing for a rather easy and intuitive setting and dispensing of a well-defined dose of a medicament. It is a further aim to provide a drive mechanism having a dose setting member and a dose dispensing member that are both located at a proximal end section of the device to improve ease of use of the device.
It is a further object to provide a drug delivery device comprising such a drive mechanism and comprising a cartridge sealed with a piston to become operably engaged with a piston rod of such a drive mechanism.